Use center of entire object as pivot point in edit mode (2.8)
I don't think the mesh has any knowledge of its object's pivot point in Edit Mode.. so to put the transform pivot at the object origin, that would be, (with 'Pivot' set to 'Cursor'),


Tab to Object Mode
ShiftS > 'Cursor to Selected'
Tab  back again.


I find it's pretty unusual, though, that I don't want my pivot at the center of some edge, face, loop, or somesuch.. in which case that can be selected, and the Cursor sent to Selected in Edit Mode.